1. Field of the Invention
This invention relates to a multi-color organic electroluminescence device, and more particularly to a multi-color organic electroluminescence device exhibiting multi-color display and a method for manufacturing the same.
2. Discussion of the Background
An organic electroluminescence (hereinafter also referred to as "EL") device is constructed so that a thin film containing a fluorescent organic compound is interposedly arranged between cathodes and anodes. The thin film is injected with electrons and holes, which are recombined with each other to generate excitons, which are then subject to deactivation, leading to light emission (fluorescence or luminescence). The organic EL device carries out display using such fluorescence or luminescence.
In order to execute multi-coloring of such an EL device basically constructed as described above, such a structure as shown in FIG. 3 is proposed by way of example. More particularly, an EL device shown in FIG. 3 includes a light-permeable substrate 100 made of glass, which is formed on an inner surface thereof with light-permeable anodes 101 in a predetermined pattern. The anodes 101 each are made of indium tin oxide (ITO). The anodes 101 have luminous layers R, G and B for emitting light of red, green and blue luminous colors arranged thereon in order, respectively, each of which is formed thereon with a cathode 102, which is made of metal such as Mg:Ag, Al:Li or the like. Such an electrode structure is arranged on the substrate 100 while being sealedly isolated from an ambient atmosphere.
In the organic EL device thus constructed, the luminous layers R, G and B are injected with electrons through the cathodes 102, as well as holes through the anodes 101. Then, the electrons and holes are recombined with each other as described above, resulting in excitons being generated. Deactivation of the excitons causes the luminous layers R, G and B to emit light, so that luminous display of predetermined colors defined by band gaps different for every luminous layers R, G and B may be provided. The luminous display thus provided is externally observed through the substrate 100.
In manufacturing of the organic EL device, an organic film of which the luminous layer is made is readily decomposed by water, resulting in formation of a display pattern by photolithography which includes a water development step being failed. Thus, in order to form the display pattern, it is compelled to utilize mask deposition techniques using a mask formed with openings in correspondence to the pattern. The mask deposition techniques are carried out using an apparatus which is so constructed that a mask and a substrate are arranged in a vacuum envelope, wherein a material is deposited on the substrate in a predetermined opening pattern through the mask.
Unfortunately, the vacuum envelope is provided therein with no means for accurately positioning the mask and substrate, so that the mask deposition techniques substantially fail to form the display pattern of the luminous layers at fine pitches.
It would be considered that arrangement of any positioning means for automatically positioning the mask and substrate in the vacuum envelope solves the above-noted problem. Nevertheless, the mask deposition techniques cause another problem. More particularly, deposition through the openings of the mask causes the material for each of the luminous layers passing through the openings to expand in a size larger than the openings, to thereby extend or get under an edge of the luminous layers adjacent thereto, resulting in the luminous layers different in kind or type from each other overlapping with each other at an edge thereof, leading to occurrence of color mixing during luminous operation of the organic ED device.
The above-described problem encountered with the mask deposition techniques that the luminous layer extends or gets under the adjacent luminous layers is not prevented unless the mask and substrate are kept intimately contacted with each other. However, intimate contact between the mask and the substrate possibly causes damage to the thin film formed on the substrate such as, for example, a hole transport layer formed on the anodes (not shown in FIG. 3) or so-called cross-contamination wherein a deposited material adhered to the mask is re-adhered to the thin film, leading to contamination of the thin film. Thus, the problem that the luminous layer gets under the adjacent luminous layers is unavoidable in the mask deposition techniques.